THE NEW BALL BEARINGS

2016-01-08

    Want to finish more than 100 yards ahead(in a 100 mile race)by simply changing the ball bearings in your hubs?Sounds too good to be true,but it's possible with today's new bearing technology.
     Available for more than 100 years,the ball bcarign has recently benefitted from several major technological innovations.As an engineer and manufacturer of ball-bearing systems for industrial use,I was naturally interested in their possibilities for the bicycling market.What follows are the results of a scientifically precise comparative experiment designed to test the utility of.these new bearing systems in bicycle hubs from two popular brands.The experiment is repeatable by any trained researcher wishing to verify(or disprove)the results.
    Part of this new bearing technology uses fiberglass-filled Teflon seals for bearings that offer numerous advantages over rubber or metal seals,increased sealability.
    What has been learned form tribology(the science of friction and wear)can be applied to the bicycle in the form of the ion deposition process.This procedure uses vacuum and an inert gas plasma with high voltage to coat bearing surfaces.It produces an ultra clean bearing surface because of argon ion bombardment just prior to applying a thin lubricant coatign.Excellent adhesion is obtained by driving the vapor atoms into the ball bearing metal surface by intermolecular adhesion.This is not a line-of-sight process;it covers components with complex geometry.Of the materials tested,lead was found to provide the lowest torque.
Testing
    Inquiries concerning the feasibility of this experiment produced comments such as:"It's impossible to measure the difference between precision bearings at speed in front and rear axle hubs,"and "The bearing torque is insignificant compared to everything else."A challenge was in the offing!
    A preliminary bench test showed that by simply changing the seal material and configuration in just the front and rear hubs,a significant performance increase could be realized,and that something so random as a speck of sand could possibly decide the out come of a 100-mile bicycle race.An energy analysis equation presented by Chester Kyle,Ph.D.shows how,as follows:
F=W*{(Crr+sin(arctan(S)}+A1V)+1/2P*C*A*(V+VW2)
where
F=Net retarding force on bicycle(lbf)
W=Total weight of bicycle and rider(186 lbf)
Crr=Tire rolling resistance coefficient(.0035)
S=Slope of course(assumed 0 for comparative purposes)
A1=Variation in rolling resistance due to velocity(.0000667)
V=Bicycle velocity(feet/second)
P=Air density slugs/Ft3(.00233@70 degrees F)
Cd=Drag coefficient(0.9)
A=Projected frontal area of bicycle and rider(4.5 feet2)
W=Wind velocity(assumed 0,for comparative purposes)
This equation reduces to the following:
F=WCrr+A1WV+1/2PCdAV2+Fsg
where:
F=WCrr(0 velosity rolling friction)
A1WV=Rolling friction at velocity correction factor 1/2PCAV2=Pressure drag
Fsg=Retarding force of front and rear axle bearings
   =Bearing torque/wheel radius
The question we were anxious to answer was:What effect do a variety of parameter was:What effect do a variety of parameters have on bearing torque;specifically,seal material and design,type of ball retainer,and lubricants?
    All that remained was to accurately measure the bearing torque.Repeatable results were obtained slightly more than a year ago using a rotating disk of known mass and inertia,and a chopper disk attached to the rotatign disk of known mass and inertia,and a chopper disk attached to the rotating disk passing through a stationary GEH21A2 light-emittign diode(LED)Once every revolution,the chopper disk breaks a light beam in the LED.
    The signal,after passing through a metrabyte P10-12 digital board,provided a graph of torque vs.rpm.The input signal,a first derivative of rpm.was processed with an IBM PC through a series of computation written in the programming language PASCAL.
   "What effect do a variety of parameters have on bearign torque;specifically,seal material and design,type of ball retainer,and lubricants?"
    Once the test flywheel was taken up to speed (400 rpm)and the external driver disengaged,the computer accurately noted the change in rpm and printed out the rpm vs.torque data for the test apparatus.The torque values were calculated from the T=I∝equation,and the rpm taken between subject calculations,Torque values were recorded at 25-rpm intervals from 400 down to 225 rpm.
    The calculations’ suggested an inertia mass of 17.36 in.-lbs.sec.2,with a weight of 105 pounds.The idea of a rotating mass in a partial vacuum offered a fair compromise between variations in lubrication characteristics in a vacuum and test repeatability.This was because of daily barometric pressure fluctuations and associated windage and friction considerations.Therefore,as a result of size restrictions(the inside diameter of size restrictions(the inside diameter of the available vacuum chamber was 20 inches),the inertia load could be only 1/4 of the load of a bicycle and rider.But with a radial load of 105 pounds and a rotational speed of 16-32 mph,the most significant performance variable could be approximated.
    The drive mechanism consisted of a DC motor mounted on 1/2-inch-diameter linear bearings while the motor was engaged and disengaged by a mechanical feed-through.The bearings were mounted on four 1-inch-diameter vertical supports.Pressure inside the vacuum was 25-inches HG,plus or minus 1/4 inches.
    For comparative purposes,the following configurations were tested.A popular brand name bicycle hub was tested with three types of bearign systems;
    Abec 1 precision,6001-size ribbon steel retainer with two rubber scals(labeled as Bearing"A"in the table).
    Above configuration with one rubber seal(Bearing "B").
    The Champion TSTL bearing.This is a phenolic tetainer,abec 7 precision bearign treated with several-thousand angstroms of lead.It also incorporates one Teflon seal on the outboard side (Figure 3).
    A stock brand name hub was then tested for comparison purposes,with its two piston-ring-type seals per side,lubricated with Bullshot grease("C").
The results of the test are shown in Figure 5.The Champion TST-L bearings consistently offer the least amount of resistant torque for the complete range of revolutions per minute.
    Each of the hub,seal,bearing combinations shows a rough linear increase in torque with rpm change,except for the No.3 configurationl.Above 350rpm,No.3 displays a nonlinear torque increase(this hub uses no retainer to fix the bearign at constant relative distances),This increase may be caused by ball-to-ball contact(    Gigure 4).In general,loose ball contact(Figure 4).In general,loose ball bearings are not as efficient as ball bearings in retainers,especially at higher speeds.
A Question of Torque
    What does the torque of just the front and rear hub ball bearigns mean to the bicycle and rider?
    And more important,what is the additional distance that a more efficient(i.e.,less resistive)bearing,seal,hub combination,would allow you to  travel while exerting no additional energy?This distance can be determined by the following equation:
Fsg=Tsg/Rw
where:
Tsg=measured bearign friction at the specific measured velocity
Rw=the radius of the wheel
Assume that all energy conserved from the more efficient bearings goes to overcome pressure drag.Thus:
Vnew=(2(Fb-Fnew)/(PCdA))^1/2
Vnew=new velosity with improved antifriction bearing system
Fb=baseline resistance forces
Fnew=new antifriction bearing systems resistance force
Thus,the distance advantage obtained from a better antifriction bearing can be determined from the following:
AD=race distance*(1-(Vb/Vnew))
where:
Vb=Baseline velosity
Outgasing of the lubricant in vacuum was not considered to be significant when inspection after testing showed the grease or oil in place.
    Keep in mind that,in general,the bearing torque becomes less significant(relative to other frictional considerations such as wind drag)at higher speeds amd more so at lower speeds.
Life testing of ion-treated spacecraft bearings has recorded many years of unattended bearing operation.More down to earth,bench and field tests have documented more than a 1,000 mile bearign life to date,with no loss in performance(Figure 6).
    Contributing factors such as the type of seal,lubricant,and retainer construction can figure significantly in ball bearing performance.
    The results of these tests clearly show a difference in performance with the three types of bearings tested.Precision lead-coated,Teflon-sealed hub bearings could easily mean the difference between winning and losing in a bicycle race.